276 research outputs found
The JCMT Gould Belt Survey: radiative heating by OB stars
Radiative feedback can influence subsequent star formation. We quantify the heating from OB stars in the local star-forming regions in the James Clerk Maxwell Telescope (JCMT) Gould Belt Survey. Dust temperatures are calculated from 450/850 ÎŒm flux ratios from SCUBA-2 observations at the JCMT assuming a fixed dust opacity spectral index ÎČ = 1.8. Mean dust temperatures are calculated for each submillimetre clump along with projected distances from the main OB star in the region. Temperature versus distance is fitted with a simple model of dust heating by the OB star radiation plus the interstellar radiation field and dust cooling through optically thin radiation. Classifying the heating sources by spectral type, O-type stars produce the greatest clump average temperature rises and largest heating extent, with temperatures of over 40 K and significant heating out to at least 2.4 pc. Early-type B stars (B4 and above) produce temperatures of over 20 K and significant heating over 0.4 pc. Late-type B stars show a marginal heating effect within 0.2 pc. For a given projected distance, there is a significant scatter in clump temperatures that is due to local heating by other luminous stars in the region, projection effects, or shadowing effects. Even in these local, âlow-massâ star-forming regions, radiative feedback is having an effect on parsec scales, with 24 perâcent of the clumps heated to at least 3 K above the 15 K base temperature expected from heating by only the interstellar radiation field, and a mean dust temperature for heated clumps of 24 K
Goonhilly: a new site for e-MERLIN and the EVN
The benefits for the e-MERLIN and EVN arrays of using antennae at the
satellite communication station at Goonhilly in Cornwall are discussed. The
location of this site - new to astronomy - will provide an almost equal
distribution of long baselines in the east-west- and north-south directions,
and opens up the possibility to get significantly improved observations of
equatorial fields with e-MERLIN. These additional baselines will improve the
sensitivity on a set of critical spatial scales and will increase the angular
resolution of e-MERLIN by a factor of two. e-MERLIN observations, including
many allocated under the e-MERLIN Legacy programme, will benefit from the
enhanced angular resolution and imaging capability especially for sources close
to or below the celestial equator (where ESO facilities such as ALMA will
operate) of including the Goonhilly telescopes. Furthermore, the baselines
formed between Goonhilly and the existing stations will close the gap between
the baselines of e-MERLIN and those of the European VLBI Network (EVN) and
therefore enhance the legacy value of e-MERLIN datasets.Comment: 10 pages, 2 figue
The JCMT Gould Belt Survey: the effect of molecular contamination in SCUBA-2 observations of Orion A
Thermal emission from cold dust grains in giant molecular clouds can be used
to probe the physical properties, such as density, temperature and emissivity
in star-forming regions. We present the SCUBA-2 shared-risk observations at 450
m and 850 m of the Orion A molecular cloud complex taken at the James
Clerk Maxwell Telescope (JCMT). Previous studies showed that molecular emission
lines can contribute significantly to the measured fluxes in those continuum
bands. We use the HARP CO J=3-2 integrated intensity map for Orion A in
order to evaluate the molecular line contamination and its effects on the
SCUBA-2 maps. With the corrected fluxes, we have obtained a new spectral index
map for the thermal emission of dust in the well-known integral-shaped
filament. Furthermore, we compare a sample of 33 sources, selected over the
Orion A molecular cloud complex for their high CO J=3-2 line
contamination, to 27 previously identified clumps in OMC-4. This allows us to
quantify the effect of line contamination on the ratio of 850 m to 450
m flux densities and how it modifies the deduced spectral index of
emissivity for the dust grains. We also show that at least one
Spitzer-identified protostellar core in OMC-5 has a CO J=3-2
contamination level of 16 %. Furthermore, we find the strongest contamination
level (44 %) towards a young star with disk near OMC-2. This work is part of
the JCMT Gould Belt Legacy Survey.Comment: 13 pages, 6 figures, Accepted for publication in Monthly Notices of
the Royal Astronomical Society (MNRAS
The Physical and Chemical Structure of Hot Molecular Cores
We have made self-consistent models of the density and temperature profiles
of the gas and dust surrounding embedded luminous objects using a detailed
radiative transfer model together with observations of the spectral energy
distribution of hot molecular cores. Using these profiles we have investigated
the hot core chemistry which results when grain mantles are evaporated, taking
into account the different binding energies of the mantle molecules, as well a
model in which we assume that all molecules are embedded in water ice and have
a common binding energy. We find that most of the resulting column densities
are consistent with those observed toward the hot core G34.3+0.15 at a time
around 10 years after central luminous star formation. We have also
investigated the dependence of the chemical structure on the density profile
which suggests an observational possibility of constraining density profiles
from determination of the source sizes of line emission from desorbed
molecules.Comment: 14 pages, accepted for publication in Astronomy and Astrophysic
Expanding e-MERLIN with the Goonhilly Earth Station
A consortium of universities has recently been formed with the goal of using
the decommissioned telecommunications infrastructure at the Goonhilly Earth
Station in Cornwall, UK, for astronomical purposes. One particular goal is the
introduction of one or more of the ~30-metre parabolic antennas into the
existing e-MERLIN radio interferometer. This article introduces this scheme and
presents some simulations which quantify the improvements that would be brought
to the e-MERLIN system. These include an approximate doubling of the spatial
resolution of the array, an increase in its N-S extent with strong implications
for imaging the most well-studied equatorial fields, accessible to ESO
facilities including ALMA. It also increases the overlap between the e-MERLIN
array and the European VLBI Network. We also discuss briefly some niche science
areas in which an e-MERLIN array which included a receptor at Goonhilly would
be potentially world-leading, in addition to enhancing the existing potential
of e-MERLIN in its role as a Square Kilometer Array pathfinder instrument.Comment: 7 pages, 3 figures, to appear in the proceedings of "Astronomy with
megastructures: Joint science with the E-ELT and SKA", 10-14 May 2010, Crete,
Greece (Eds: Isobel Hook, Dimitra Rigopoulou, Steve Rawlings and Aris
Karastergiou
APECS - The Atacama Pathfinder Experiment Control System
APECS is the distributed control system of the new Atacama Pathfinder
EXperiment (APEX) telescope located on the Llano de Chajnantor at an altitude
of 5107 m in the Atacama desert in northern Chile. APECS is based on Atacama
Large Millimeter Array (ALMA) software and employs a modern, object-oriented
design using the Common Object Request Broker Architecture (CORBA) as the
middleware. New generic device interfaces simplify adding instruments to the
control system. The Python based observer command scripting language allows
using many existing software libraries and facilitates creating more complex
observing modes. A new self-descriptive raw data format (Multi-Beam FITS or
MBFITS) has been defined to store the multi-beam, multi-frequency data. APECS
provides an online pipeline for initial calibration, observer feedback and a
quick-look display. APECS is being used for regular science observations in
local and remote mode since August 2005.Comment: 4 pages, A&A, accepte
The JCMT Gould Belt Survey: radiative heating by OB stars
This is the final version. Available from Oxford University Press via the DOI in this recordRadiative feedback can influence subsequent star formation. We quantify the heating from OB stars in the local starforming regions in the JCMT Gould Belt survey. Dust temperatures are calculated from 450/850 ”m flux ratios from
SCUBA-2 observations at the JCMT assuming a fixed dust opacity spectral index ÎČ = 1.8. Mean dust temperatures
are calculated for each submillimetre clump along with projected distances from the main OB star in the region.
Temperature vs. distance is fit with a simple model of dust heating by the OB star radiation plus the interstellar
radiation field and dust cooling through optically thin radiation. Classifying the heating sources by spectral type,
O-type stars produce the greatest clump average temperature rises and largest heating extent, with temperatures
over 40 K and significant heating out to at least 2.4 pc. Early-type B stars (B4 and above) produce temperatures of
over 20 K and significant heating over 0.4 pc. Late-type B stars show a marginal heating effect within 0.2 pc. For
a given projected distance, there is a significant scatter in clump temperatures that is due to local heating by other
luminous stars in the region, projection effects, or shadowing effects. Even in these local, âlow-massâ star-forming
regions, radiative feedback is having an effect on parsec scales, with 24% of the clumps heated to at least 3 K above
the 15 K base temperature expected from heating by only the interstellar radiation field, and a mean dust temperature
for heated clumps of 24 K.Science and Technology Facilities Council (STFC
Interferometric multi-wavelength (sub)millimeter continuum study of the young high-mass protocluster IRAS05358+3543
The young massive star-forming region IRAS05358+3543 was observed at
high-spatial resolution in the continuum emission at 3.1 and 1.2mm with the
Plateau de Bure Interferometer, and at 875 and 438mum with the Submillimeter
Array. We resolve at least four continuum sub-sources that are likely of
protostellar nature. Two of them are potentially part of a proto-binary system
with a projected separation of 1700AU. Additional (sub)mm continuum peaks are
not necessarily harboring protostars but maybe caused by the multiple molecular
outflows. The spectral energy distributions (SEDs) of the sub-sources show
several features. The main power house mm1, which is associated with CH3OH
maser emission, a hypercompact HII region and a mid-infrared source, exhibits a
typical SED with a free-free emission component at cm and long mm wavelengths
and a cold dust component in the (sub)mm part of the spectrum (spectral index
between 1.2mm and 438mum alpha~3.6). The free-free emission corresponds to a
Lyman continuum flux of an embedded 13Msun B1 star. The coldest source of the
region, mm3, has alpha~3.7 between 1.2mm and 875mum, but has lower than
expected fluxes in the shorter wavelength 438mum band. This turnover of the
Planck-function sets an upper limit on the dust temperature of mm3 of
approximately 20K. The uv-data analysis of the density structure of individual
sub-cores reveals distributions with power-law indices between 1.5 and 2. This
resembles the density distributions of the larger-scale cluster-forming clump
as well as those from typical low-mass cores.Comment: 13 pages, 7 figures, accepted for Astronomy and Astrophysics, a
high-resolution version of the paper is also available at
http://www.mpia.de/homes/beuther/papers.htm
Optical and Near Infrared Study of the Cepheus E outflow, a very low excitation object
We present images and spectra of the Cepheus E (Cep E) region at both optical
and infrared wavelengths. Only the brightest region of the southern lobe of the
Cep E outflow reveals optical emission, suggesting that the extinction close to
the outflow source plays an important r\^ole in the observed difference between
the optical and IR morphologies. Cep E is a unique object since it provides a
link between the spectroscopic properties of the optical Herbig-Haro (HH)
objects and those of deeply embedded outflows.Comment: Accepted Astron. J., 8 files: paper, tables plus 6 figure
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